Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015

278 EDINBURGH GEOLOGICAL SOCIETY. southerly, so that different members of the series are brought in turn against the Skiddaw Slates. This appears to be due to a north and south fault running along this line, and having a downthrow to the west. As regards the origin of the depression in which Derwent­ water is situated, there can be no doubt but that it is to be ascribed to the agency of the ordinary denuding forces, and especially to the action of glaciers, unmistakable traces of which are universally visible. No one, however, who studies the region can doubt that the denuding forces have been directed and powerfully assisted by the peculiarities in the physical geo­ logy of the district. The greater part of the lake has been scooped out of the soft Skiddaw Slates, the resisting Green Slates and Porphyries simply fringing a portion of one side. As I have shown, this difference in the structure of the two sides of the lake is due to the existence of powerful faults. In so far, there­ fore, as this difference in structure has enabled the powers of the denuding agents to be more efficiently applied, and in so far as their course has been determined by this difference, in so far are we justified in asserting that the origin of the valley may be ascribed to the existence of faults as one cause. No one, as far as I am aware, believes that valleys are ever the result of open fissures produced by faulting, though a misconception to this effect is apparently held by some. On the contrary, it is simply held that faults constitute lines of weakness, along which denuding agencies meet with less resistance than elsewhere; and the line of weakness is not caused by the existence of an open fissure, but is due to the apposition of strata of unequal hardness, con­ sequent on the displacement, and also to the inevitable breakage and comminution of the rocks which must occur along every line of dislocation. In this sense, I think, it will be very diffi­ cult to show that faults are not in many cases connected with the formation of valleys in mountainous countries; at the same time that there are, doubtless, many valleys in which no displace­ ment of the strata has occurred.

II. Notes on the Geology of Southerness, Kirkcudbrightshire. By WILLIAM JOLLY.

(Abstract.) Parallel to the Silurian and Old Eed Sandstone belts of Scot­ land, and running from north-east to south-west, stretches a narrow stripe of Carboniferous strata from the head waters of the Liddel, at the junction of the Cheviots and the Lowthers, to Locher Moss, in the south of Dumfriesshire. This line of the. Coal Measures disappears under the Solway at the mouth of the Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015

ON THE GEOLOGY OF SOUTHERNESS. 279

Nith, forming there the extended Blackshaw Bank, but reappears at two points in Galloway, in the same line of strike. On,e of these is at Southerness, and forms a rough triangle, of which the Ness is the apex, a narrow patch of but a few miles in extent, but rich in fossils and geological points of interest. The other is at Abbey Head, east of Kirkcudbright Bay. These two little patches of the Coal-Measures seem at first sight strange and isolated, as lying apart in the wide Silurian district of Galloway; but their strangeness and isolation at once disappear when they are seen to form part of a Carboniferous belt that stretches from the Northumberland coal-field to Abbey Head in Kirkcud­ bright ; a belt, the counter part and parallel of a smaller patched belt stretching from Girvan to Dunbar on the north; and in­ teresting, moreover, as remnants of the great Carboniferous sheet that probably once covered the wide Silurian uplands of the south of Scotland. The Carboniferous belt just spoken of is, according to the new geological map of Murchison and Geikie, the Carboniferous Limestone series, which lies above the Lower Carboniferous or Calciferous Sandstones, and below the millstone grit and True Coal-Measures. Along this shore the Carboniferous Limestone series is repre­ sented by different limestones, shell, coral, and encrinital sand­ stones, shales, and seams of coal and ironstone, variously intermingled, and laid beautifully open for inspection by the restless action of the Solway waves. Of the whole shore we made a careful survey. The shore is skirted by a high cliffy bank at various distances from tide-mark, clothed with shrubbery and grass, that once formed the old coast line. Underneath this cliff stretches the rocky shore, washed by the daily tides, exhibiting a belt of Carboniferous strata. The rocks are of different heights, and variously sloped and contorted, always jagged and dark, sometimes rising high and striking, and then sinking under the fine sand of the Firth. The most interesting portion of these rocks lies between Bor- ron Point and the Thirlstone, stretching to equal distances on both sides of the gardener's house of Arbigland, which forms the centre of observation. The limestone is found chiefly between the gardener's house and Borron Point; the coal and iron south of the Thirlstone; the sandstone all along the shore, but best at and near the Thirlstone; the shales everywhere, but more be­ tween the Thirlstone and the Great Boulder, a little south of the gardener's house. South of his house the old coast line becomes the present sea cliff, and has been worn into caves, and hollowed into various picturesque masses by the fierce waves that roll in from the Irish Sea. South of the Thirlstone the rocks leave the beach and run across Gillfoot Bay, which is sandy, but again Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015

280 EDINBURGH GEOLOGICAL SOCIETY. strike the coast at Southerness, where they form the shore, but soon again disappear in the wide waste of the Mersehead Sands. It is this carboniferous shore that exhibits the notable pheno­ mena to which we would now shortly direct your attention, and from which the specimens we exhibit have been brought. The Variety of the Strata.—One of the first features that strikes a visitor is the varied character of the rocks exposed, their sudden transitions, and strange interminglings. Here in a walk of a mile or two we pass over a varied succession of granite, Silurian slate, carboniferous sandstone, shale, limestone, iron­ stone, coal, and trap; while the shore is strewed with boulders (and rocks) of various size, representatives of the inland rocks, brought thither by the glaciers of the past. All these are beau­ tifully exposed and laid open for inspection in successive lines, like as in a great seaside museum, in which a tyro in the science might learn to distinguish the different kinds of rocks. Variations in Dip and Strike, Slip.—Another feature of this shore is the remarkable and sudden variations in the dip and strike of the various rocks that skirt it. It is almost impos­ sible to give any one direction as the general one; but they incline more to run from north-east to south-west than in any other direction that is in the line of the general strike of the Carboniferous belt. But they look towards every point of the compass. North of Borron Point the strike goes variously north­ west ; immediately south of it they sweep round to north-east; towards the gardener's house they turn round again towards the north-west, but some run nearly north and south; south of the house they strike east and west; opposite the garden gate a new series Suddenly interrupts the others, and runs south and east, and this continues unchanged for a considerable distance till south of the Thirlstone the strata abruptly take a north-east direction, only to be again and again interrupted by some new and abrupt strike. The rocks have a tendency to sweep in great circles, as seen at Borron Point, and in both sides of the gardener's house. But at two points the strata take the form of very complete concentric circles. One of these lies a little north of the gardener's house. Unless seen, it could not be thought that such a beautiful cir­ cular section of rocks could be shown in so small a space. The other concentric series is near the Arbigland Boulder, south of the gardener's house; but though evident enough, it is not so remarkable as the other to the north, and cannot be looked down on from above in the same way. The change of dip of the rocks is as varied and sudden as that of the strike. They lie at every angle from horizontal to per­ pendicular; they have even been thrown to a wide angle over the perpendicular. This variation in dip, even in the same seam, is Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015

ON THE GEOLOGY OF SOUTHERNESS. 281 well seen at Borron Point, where one sandstone bed runs very nearly north and south, quite erect and high, like a long black artificial wall. " Troubles" are plentiful, other rocks suddenly appearing in the midst of any one formation, and it is often impossible to say which is the original rock, so numerous and mixed are the seams. Of this a very fine example may be seen near the Great Boulder, where the rock has been thrown in every direction, and is com­ posed of every material in the most incredible manner. " Slips" are common, and some very fine examples are shown. One in particular occurs, just at Borron Point, and runs in a right line, as if drawn by a ruler from south-east by south to that cape. Here the amount of displacement may be measured, the various seams on each side of the slip being distinctly seen standing up and bared by the action of the waves. "Dykes" are abundant of trap and greenstone, and rise literally like dykes striking, like the great Chinese wall, right across all obstacles, but unlike it not surmounting them, but cutting right through them. The sandstone near the Thirlstbne is remarkable also as ex­ hibiting folds and plications similar in a great degree to those of the Silurian rocks. They have been crushed up into those wave­ like bends, so well known in slate rock, but rarer in sandstone. Carboniferous Limestones.—The fossil remains most beautifully exhibited along this shore are those of corals. The most ex­ quisite specimens may be gathered of Liihostrotion Portlockii, L. cylindricum, L. fasciculatum, and other varieties. Whole beds of these corals may be seen, with the dome-shaped masses in natural form and position as they lived, rising like the bosses of shields above the general surface of the rocks on which they rest. Some of the masses of L. Portlockii have been beauti­ fully cleaned out by their alternate wetting and drying by the sea, and by the action of the weather, except where they have, from long exposure, been rubbed with the stones of the beach. They exhibit in perfection the most beautiful honey-comb surface, with the interior radiation perfectly preserved in some of the specimens shown. Corals are the chief fossil productions of the shore. Some of them are of immense size, and I know no other spot where they may be seen in such fine condition. Ripple-marks, Worm-castings.—Various other interesting phe­ nomena are seen along this shore. Fine examples of ripple- marks on the sandstone, covered also with worm-tracks over a large surface, occur near the Thirlstone, and some fine ones near Borron Point. Some seams of sandstone show annelide borings, similar to those on the Bathgate Hills. On various sandstone surfaces along the shore certain remarkable hollows and indenta­ tions are frequent, that seem to have been the base or nest of the Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015

282 EDINBURGH GEOLOGICAL SOCIETY. worm borings, and some of them run horizontally for a consider­ able distance. South of Borron Point the indentations are as large as the palm of the hand, and palmated in shape, and occur so regularly in lines over a large surface, that they look like the prints of some gigantic reptile impressed in tenacious mud. They have likely some connection with borings, but their great size makes this doubtful. On other surfaces decided worm-castings of varied thickness, length, and character are abundant; some near the Great Boulder being close, thick, and large ; others, near Borron Point, being small and interlacing, the whole surface show­ ing a pretty appearance. These things are seen elsewhere, but here the surfaces on which they are shown are so finely bared and so extensive that they become very striking. They look almost as if they had been left by the morning tide. Fossils Found.—The following is a list of some of the fossils found in the Carboniferous strata along this shore, made out from the fossils gathered by my friend Mr Linn of Whitburn, a mem­ ber of the Society, and myself. This list sufficiently established that the carboniferous rocks here exhibited are rightly coloured by Sir R Murchison and Mr Geikie, as members of the Carboni­ ferous Limestone series ; for all those found belong to the lime­ stones of this series, as developed in, other parts of the country. The list is very partial, but it is sufficient to prove the horizon of the strata, and the rich fossil field there laid open to view by the waves of the Solway tides.

List of Fossils from Carboniferous Strata on Arbigland Shore:—

Corals. Athyris ambigua. Lithostrotion Portlockii. Streptorhynchus crenistria. irregulare. Spirifera trigonalis, and others. cyliiidricum. Sanguinolites. fasciculatum. Conularia quadriculata. junceum. Bellerophon Urii. Zaphrentis cylindrica. Loxonema. Clisiophyllum turbinatum. Euomphalus catillus. Aulophyllum fungites. Natica. Fenestella plebeia. Macrocheilus. Stenopora fumida. Nerita. Archaeocidaris Urii. Orthoceras. Actinocrinus stems. Goniatites diadema. Poteriocrinus do. Dentalium priscum. ingens. Shells, etc. Edmondia sulcata (?)

# PorceUia Armata. Annelide burrows. * Productus longispimis. Palatal tooth—large—of—(?) Martinii. Cauda-Galli. punctatus. Few land plants—large Stigmaria scabriculus. exposed in rock at Thirlstone, semireticulatus. also at Borron Point. Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015

ON THE GEOLOGY OF SOUTHERNESS. 283

Sea Action is well seen all along the shore, especially near the Thirlstone, where it has formed "stacks" and natural arches, and hollowed out large caves. One thing deserving of notice near the same cape is the great number of "pots" formed in the sandstone by stones rotating and revolving under the action of the sea-water, as is seen so often in river beds, especially near waterfalls, as at Eumbling Brig and Caldron Linn, on the Devon, beyond Dollar. In the matter of grand and picturesque cliff' scenery, few coasts could surpass the " Craigs of Colvend," of hard Silurian, which are equal to, if they do not surpass, the cliffs of the Forfarshire and Caithness coasts, and which have been rendered classical, as exhibiting the scenery of "Guy Mannering." No one should visit that district without walking along the high cliff road between Southwick and Colvend. Glacial Remains.—The whole of the* low lands below the Criffel range are covered with a very thick deposit of boulder clay, consisting of gravel, clay, and sand. The sand, gravel, and boulders are always granitic, showing that the deposit has been carried down from the granite heights to the sea. It lies in great thickness, in wide flats, and dome-shaped mounds, espe­ cially towards the base of the hills, and forms a striking element in the scenery. Kirkbean lies in a basin-shaped hollow, amidst glacier deposits 60 or 70 feet high, which have been cut through by the Kirkbean and Preston Mill burns. Between Kirkbean and Dalbeattie the very best illustrations of the local character of the deposit may everywhere be seen. Between New Abbey and Kirkbean remarkably fine examples of such deposits occur, consisting of hillocks so rounded that they look like artificial mounds. The very soft character of their contents is proved by the deep excavations made by the smallest streamlets. Near Hillhead, in the Drum Burn, a very fine example of a deep valley excavated in these superficial deposits occurs, and is all the more striking that it is now entirely without water. Travelled blocks are very abundant, a remarkable one, called the " Arbigland Boulder," being known to local fame. Splendid granite blocks are scattered on the side of Criffel above Loch Kinder, and cause astonishment at their number and immense size. They are all more or less angular, being of granite, carried but a short distance, having, in fact, come from the Criffel range, on the side of which they lie. Loch Kinder is remarkable also as being an example of a lake barred back by glacial debris, the waters being kept in at two ends by gravelly accumulations, but resting on the granite at other points. On the north side very little would send its whole mass of water into the Abbey Pow Burn. Recent Deposits.—Good examples of these occur in this interest­ ing corner. We have sandhills along the shore near Souther- Downloaded from http://trned.lyellcollection.org/ at Nanyang Technological University on April 26, 2015

284 EDINBURGH GEOLOGICAL SOCIETY. ness. West of Southemess we have an example of the true merse land or salt marsh, with its peculiar herbage, grazed on by many cattle, and which is the home of the gull, and the oyster-catcher, the kittywake and the curlew, the heron and the plover. A recent deposit of thick moss of a strange composition occurs below Carsethorn, and has been dyked back from the inroads of the sea by a strong stone bulwark.

Thursday, 1st April 1869.

JAMES POWRIE, Esq. of Ees wallie, F.G.S., F.E.S.E., Vice-President, . in the Chair.

The following Communication was read:—

On the Earliest known Vestiges of Vertebrate Life;—being a Description of the Fish Remains of the Old Red Sandstone Rocks of Forfarshire. By JAMES POWRIE, F.G.S., F.E.S.E. (Illustrated by five quarto Plates, Nbs. X. to XIV. inclusive.) The middle Ludlow beds, in the neighbourhood of Leintwar- den, have, I believe, yielded the earliest vestiges of vertebrate life, a fragment of Pteraspis, or at least of a closely allied genus, having been discovered there some time ago. In the upper Ludlow rocks and Downton beds ichthyic remains become abund­ ant, but in a sadly imperfect condition. In these localities, asso­ ciated with Pterygotus, Platyschisma helicites, Lingula cornea, &c, are remains of the Cephalaspidee; while the Ludlow and Downton bone-beds are full of broken fragments of bones, spines, detached scales, and such like. The cornstones of Hereford have, been found to contain similar remains. The Cephalaspid remains are for the most part readily recognised, all the rest are so broken up and fragmentary that, but for the light our Scottish Old Eed Sandstone rocks have cast on these olden fishes, their nature and relations would have been comparatively unknown. None of our Scottish rocks affording fish remains are older than the lowermost beds of the Old Eed Sandstone, and hence not so ancient as those of the above mentioned English localities, which, as Platyschisma helicites, Lingula cornea, and Beyrichia are also common to the Lesmahagow Upper Silurian or Passage Beds, appear to belong to a period immediately antecedent to that of the Scottish rocks affording our earliest known fish remains. Cephalaspis has long been known as a characteristic fossil of the Forfarshire Sandstones. Pteraspis was first discovered in Scot­ land by the Eev. Hugh Mitchell, in a quarry near Bridge of